1. Field of the Invention
The present disclosure is generally related to communication systems, and, more particularly, is related to wireless communication systems and methods.
2. Related Art
Wireless communication systems are widely deployed to provide various types of communication, such as voice, data, and so on. Much has changed in the way of wireless devices from the early days of bulky walkie-talkies and base-mounted car phones. Miniaturization of components and advancements in protocols and methods over the years have resulted in cell phones that can rest on an ear lobe, multi-media entertainment devices like the IPOD that provide hours of entertainment while fitting comfortably in the palm of one's hand, or digital cameras that can store and transmit literally hundreds of pictures.
Consumers desire low-profile devices, but not at the expense of performance. For instance, consider cell phones. Consumers generally prefer to have long-lasting operation in terms of battery power while retaining the ability to pick up their phone at any time or location and enjoy optimal reception. However, these performance features are often subject to competing interests. That is, current technology implements roaming to determine the proximity to various stations (e.g., peer stations or access points). Roaming may be performed during periods that a consumer is engaged in a call, or during standby (e.g., when the consumer is not engaged in a call), and typically is implemented using active scanning or passive scanning.
In passive scanning, the station (e.g., as embodied in a cell phone) may read from an access point list (e.g., temporarily loaded into memory of the station from an access point through the most recent association), and then tune into the various channels corresponding to the listed access points. At each tuned channel (e.g., frequency band), the station waits and listens for a beacon. Beacons are typically sent every 100 milliseconds (msecs). When the beacon is received, the station can determine the suitability (reliability of the signal reception, and often correlated with the proximity) of the access point for potentially future association. Such a determination may be made by evaluating the signal strength according to techniques well-known to those having ordinary skill in the art. Through this process, the access point list is narrowed to a candidate list of suitable access points for potential future association (e.g., when the consumer decides to make a call, or when passage to a different cell is to take place). However, this process of tuning, waiting (e.g., 100 mscec), determining, tuning, waiting, etc. can be time-consuming, and consequently can impose a significant drain on the battery of the station, especially in standby mode.
Active scanning is typically an improvement in speed over passive scanning, and generally entails the station sending out a probe request (e.g., a broadcast frame) on channels identified in the access point list. All access points that receive the probe request prepare a probe response frame for transmission back to the station. However, this technique is also time-consuming since the probe request is typically a long frame comprising a substantial amount of information, and further because the frame is sent at a low frame rate to ensure that all access points from the list are reached. Adding to the delay is the preparation and reply transmission time at the access point (e.g., typically 2-4 msecs).